This invention relates generally to needles used in medicine and more particularly to a needle assembly having a depth stop to limit penetration of the needle into the subject, which depth stop can be selectively removed from the needle.
In some medical applications needles are used to make relatively deep penetrations into the body in order to perform their tasks. For instance where it is necessary to obtain a biopsy sample, the needle may have to penetrate deep inside tissue to the location from which the sample is to be taken. However, there are also situations where the needle has to penetrate a substantial distance through tissue in order to inject a drug or withdraw fluid. One specific example is that of accessing the intramedullary canal of bone. This may be done to collect a specimen of bone marrow or fluid from the intramedullary canal. It is also possible that a drug or other fluid may be infused into the canal through the needle.
To penetrate the hard cortical bone surrounding the intramedullary canal, the needle must be hard and strong, and substantial force has to be applied to the needle. The needle is typically mounted on a handle that can be grasped by a medical technician to supply the necessary force to penetrate the cortical bone to reach the intramedullary canal. It is important that the medical technician exercise care so that the needle is not driven elsewhere in the body other than the target bone. Depending upon the location of the bone selected for penetration, the bone may be near to organs or blood vessels that could be damaged by a misdirected needle. For example, if the needle penetrates too deeply, it could damage an untargeted area of the body. Thus, the use of a bone needle assembly of this type requires the simultaneous exercise of substantial force and precision.
One way to reduce the chance that the needle will damage the body is to provide a depth stop that limits the depth of penetration of the needle into the body. Typically the depth stop is disposed around the needle below the handle and can engage the exterior of the body to stop the inward thrust of the needle. The depth stop reduces the length of the needle that is available for penetrating into the body. The appropriate depth of penetration can vary widely from one patient to the next. For example, an obese patient may require penetration of several inches of skin and soft tissue to reach the bone, while a thin patient requires very little penetration to reach the bone. Moreover, the location of the target bone may call for a different depth of penetration. To meet this need, depth stop units have been provided that permit the depth stop to be adjusted to expose a greater or lesser length of the needle for penetration into the body. While these adjustable depth stop units provide greater flexibility they do not fully meet the need for variability in needle length. Moreover, some procedures have less reason to use the depth stop than others. Medical technicians differ on their preference for use of needle assemblies incorporating depth stops.
In instances where a depth stop is present in the needle assembly, a substantial length of the needle will never be available for use to penetrate into the body because it will remain covered by the depth stop. This is true even if the depth stop is adjusted to expose the maximum possible length of the needle for penetration. Accordingly, it is necessary to keep on hand multiple needle assemblies having different lengths and/or needle assemblies that do not have depth stops.